The perforation of plastic films by electrically generated sparks is known from U.S. Pat. No. 4,777,338. A plurality of electrode-counter electrode pairs is provided, between which the plastic film is guided and across which high-voltage energy is discharged. The film is moved through a water bath, and the temperature of the water bath is utilized to control the size of the perforations.
Another method for producing pores in plastic films is known from U.S. Pat. No. 6,348,675 B1. Pulse sequences are generated between electrode pairs, with the plastic film interposed therebetween, the first pulse serving to heat the plastic film at the perforation point and the further pulses serving to form the perforation and to shape it.
From U.S. Pat. No. 4,390,774, the treatment of non-conductive workpieces by electrical means is known in the sense of cutting the workpiece or welding the workpiece. A laser beam is directed onto the workpiece which is moved during the exposure, and a high voltage is applied to the heated zone using two electrodes to form an arc which serves to process the workpiece. When the workpiece is cut, it burns in a controllable manner. When workpieces are to be welded, streams of reactive or inert gas are additionally directed to the heated zone to react with either the workpiece or the electrode or a fluxing agent. In this way, glass, paper, cloth, cardboard, leather, plastics, ceramics, and semiconductors can be cut, or glass and plastics can be welded, rubber can be vulcanized, and synthetic resins can be cured thermally. However, the equipment is too clunky by its nature as to permit thin holes to be formed in the workpiece.
From WO 2005/097 439 A2 a method is known for forming a structure, preferably a hole or cavity or channel, in a region of an electrically insulating substrate, in which energy, preferably in form of heat, also by a laser beam, is supplied to the substrate or region, and a voltage is applied to the region to produce a dielectric breakdown there. The process is controlled using a feedback mechanism. It is possible to produce thin individual holes one after the other, however it is not possible to employ a plurality of electrode pairs simultaneously. Parallel operating high-voltage electrodes mutually influence each other and do not permit individual control.
From WO 2009/059786 A1 a method is known for forming a structure, in particular a hole or cavity or channel or recess, in a region of an electrically insulating substrate, in which stored electrical energy is discharged across the region and additional energy, preferably heat, is supplied to the substrate or the region to increase electrical conductivity of the substrate or region and thereby initiate a current flow, the energy of which is dissipated in the substrate, i.e. converted into heat, wherein the rate of dissipation of the electrical energy is controlled by a current and power modulating element. An apparatus for simultaneously producing a plurality of holes is not disclosed.
WO 2009/074338 A1 discloses a method for introducing a change of dielectric and/or optical properties in a first region of an electrically insulating or electrically semi-conducting substrate, wherein the substrate whose optical or dielectric properties are irreversibly altered due to a temporary increase in substrate temperature, optionally has an electrically conductive or semi-conductive or insulating layer, wherein electrical energy is supplied to the first region from a voltage supply to significantly heat or melt parts or all of the first region without causing an ejection of material from the first region, and wherein furthermore, optionally, additional energy is supplied to generate localized heat and to define the location of the first region. The dissipation of electrical energy manifests itself in form of a current flow within the substrate.
The dissipation of the electrical energy is controlled by a current and power modulating element. Alterations in substrate surfaces produced by the method also include holes produced in borosilicate glass or silicon substrates which had been provided with an insulating layer of paraffin or a hot melt adhesive. Also, holes are produced in silicon, in zirconia, in sapphire, in indium phosphide, or gallium arsenide. Partially, the discharge process was initiated by laser beam irradiation at a wavelength of 10.6 μm (CO2 laser). Grids of holes are also disclosed, but with relatively large spacings of the holes. An apparatus for simultaneously producing a plurality of holes is not disclosed.
From DE 28 30 326 A1 an arrangement is known for effecting superfine perforation of film-like sheeting using high-voltage pulses. The sheeting is passed, in a substantially contactless manner, between a pair of electrodes to which a high voltage is applied. The two electrodes are composed of multi-row needle arrays. The mutually opposing needles in the needle arrays are connected in pairs to separate excitation circuits, via control lines. The spark discharge between the two needles produces a microscopic perforation hole along the breakdown in the film-like material.
Therefore, it is clear from prior art how to perforate foils and thin sheets of dielectric materials using a high-voltage electric field of appropriate frequency or pulse shape. Local heating of the material reduces the dielectric strength at the points to be perforated, so that the applied field strength is sufficient to cause an electric current to flow across the material. If the material exhibits a sufficiently large increase in electrical conductivity with temperature, as is the case with glasses, glass-ceramics, and semi-conductors (also with many plastics), the result is an “electro-thermal self-focusing” of the perforation channel in the material. The perforation material is getting hotter and hotter, current density increases until the material is evaporated and the perforation is “blown open”. However, since the perforation is based on a dielectric breakdown, it is difficult to exactly match the desired location of the breakdown. It is known that e.g. atmospheric flashes follow a very irregular course.
CPU chips have several hundred contact points distributed over a small area on the bottom surface thereof. In order to produce supply lines to the contact points, thin sheets (<1 mm) are used, i.e. fiberglass mats coated with epoxy material referred to as “interposers”, through which the supply lines extend. To this end, several hundred holes are placed in the interposer and filled with conductive material. Typical hole sizes range from 250 to 450 μm per hole. There should not be any alterations in length between CPU chip and interposer. Therefore, the interposers should exhibit a thermal expansion behavior similar to that of the semiconductor material of the chip, which, however, is not the case with previously used interposers.
What is also lacking in the prior art is the manufacturing of a multiplicity of thin holes adjacent to one another on an industrial scale, with hole-to-hole spacings ranging from 120 μm to 400 μm, and using the electro-thermal perforation process.